1. Field of the Invention
The present invention generally relates to a multicolor lithographic rotary press. More particularly, the present invention relates to a multicolor lithographic rotary press which includes B--B type printing sections with divided plate cylinders and dampening means through which a double-width printing paper is successively passed to perform printing operation. In detail the present invention relates to a multicolor rotary lithographic press provided with a plurality of width adjusting means for adjusting the width of the printing paper and a driving roller as an assistance of the width adjusting means. Further each of the printing sections is provided with a registering system for exact placing of lines, images, colors.
2. Description of the Prior Art
A typical conventional lithographic rotary press adapted for a multicolor printing system is, for example shown in FIG. 14 which is a schematically elevational view. This conventional lithographic printing system comprises a plurality of printing sections P each of which includes two pairs of a combination of a plate cylinder PC and a blanket cylinder BC. The blanket cylinders BC of each printing section P are vertically arranged to be in contact with each other. In this conventional printing system, four sets of the printing sections P are horizontally arranged in parallel as shown in FIG. 14. A paper web W is also horizontally travelled through the printing sections in which the paper web W is successively passed between the pairs of the blanket cylinders BC, BC to print both sides of the paper web W.
Another conventional lithographic rotary press for a multicolor printing system is shown in FIG. 15. In this drawing, four printing sets each of which is composed of a plate cylinder PC and a blanket cylinder BC are radially arranged about an impression cylinder IC as a common center cylinder. The blanket cylinders BC are respectively in contact with the impression cylinder IC to form printing sections P. A paper web W is roundly travelled along the circumference of the impression cylinder IC so that the paper web W is successively passed through the four printing sections P defined between the blanket cylinders BC and the impression cylinder IC to print one side of the paper web W.
In recent years, many newspaper publishers have progressed to print newspaper in multicolor inks and thus demanded to perform such the multicolor printing on many pages at a high speed in a limited printing space.
In order to satisfy such the demands, other conventional lithographic rotary presses for a multicolor printing system have been proposed as shown in FIG. 16 and FIG. 17. In these printing systems, each printing section P includes two sets of a blanket cylinder BC and a plate cylinder PC which are symmetrically arranged so as to bring the blanket cylinders BC into contact with each other. A paper web W is vertically travelled through the four printing sections P to print both sides of the paper web W in the same manner as the above described systems. This type printing system is for example shown in "IFRA Newspaper Techniques English Edition", pp. 64 to pp. 73; April, 1988 published by INCA-FIEJ Research Association.
On the other hand, one specific type of multicolor printing apparatus in which a plurality of printing sections are isolated and vertically arranged in multisteps, and which is provided with plural registering and adjusting means to minimize the register errors among lines, images and colors generated by each of the printing sections has been well known in for example Japanese Patent Application Open Publication No.3-1946. The adjusting means of this conventional apparatus includes a shifting mechanism for each plate cylinder of respective printing sections to shift the plate cylinder in its axial direction with respect to a-blanket cylinder.
In conventional art, a B--B type printing apparatus has been also well known. This type apparatus includes four blanket cylinders each of which is accompanied with a plate cylinder and each pair of which are opposed to each other and can be moved in close to and apart from. According to this arrangement, both sides of a paper web are printed on the same occasion.
A general concept of a divided plate cylinder has been well known by one skilled in this art. The divided plate cylinder has a structure that a plate cylinder is divided into two section along its axis, each of which can be independently rotated about the axis with each other.
In cylinder arrangement methods such as a true-rolling cylinder arrangement method and an equal cylinder diameter method, skilled artisans know that the diameter of the plate cylinder arranged with a printing plate is slightly different from that of the blanket cylinder arranged with a blanket.
When a plate cylinder with a printing plate and a blanket cylinder with a blanket are adjacently arranged and driven in the counter directions at the same rotating speed by driving and driven gear units having the same pitch circle diameter and the same gear ratio, and the diameter of the arranged cylinder connected to the driving gear unit is larger than that of the cylinder connected to the driven gear unit, the circumferential surface of the cylinder connected to the driven gear unit sometimes runs idle. In detail, since the circumferential surface of the driven cylinder (blanket cylinder) tends to rotate at the same speed of the driving cylinder (plate cylinder) when they are in contact with each other, the driven cylinder is out of the control function of the driven gear unit. That is, the driven cylinder rotates regardless of the rotating force through the driven gear unit within an allowable phase range corresponding to the backlash of the gear units. The contact phase between the driving cylinder and the driven cylinder is easily affected by an instantaneous change in the contact pressure between these cylinders. This will cause an undesirable idle rotation of the driven cylinder.
In order to produce a clear and sharp printed matter the printing image and line from the plate cylinder must be always transferred to the same place on the blanket cylinder. The above described idle rotation of the blanket cylinder affects the transferred position. In other words, the idle rotation of the blanket cylinder is one of the causes for generating an unclear image such as a double image.
In a conventional B--B type printing apparatus having an ordinary type plate cylinder, Japanese Patent Application Open Publication No. 61-182951 is one of prior arts to prevent the blanket cylinder from generating the idle rotation.
Further, Japanese Patent Application Open Publication Nos. 1-313247 and 2-13559 disclose an improved roller which comprises a support shaft fixed on a stationary member, an outer tubular member rotatably supported by the support shaft and a rotatable member capable of relatively rotating with respect to the stationary member. The outer tubular member and the rotatable member are rotated about the support shaft by electric power.
Paper webs used in various printing systems are generally produced in such manner that pulp fibers are mechanically cut and broken into fine particles; dispersed in water; dehydrated and dried; and finally adhered by hydrogen-bond to form paper in a web or sheet figure. Under moisture condition, each of pulp fibers tends to extend a little less than 1 percent in its longitudinal direction and 20 to 30 percent in its radius direction. Thus paper web is extended in its longitudinal and width directions by dampening and/or watering operation. Most of the pulp fibers of general mechanically produced paper webs are orientated in the longitudinal direction of paper web, so that paper webs are remarkably extended in their width direction.
In a specific lithographic printing system employing dampening operation in printing section, a paper web is swelled by the water supplied during the dampening operation. Therefore the image and lines printed on the paper web are also deformed in response to the swell of the paper web. In the printing systems including at least two lithographic printing sections each of which is associated with dampening means to successively print color images on the same paper web, the printed images or lines formed at the first printing section are not correctly coincided with the images or lines formed at the second and later printing sections. Accordingly, this will produce printed materials with a poor quality.
The conventional technique shown in the aforesaid Japanese Patent Application Open Publication No. 3-1946 provides a width adjusting mechanism to minimize the generation of register errors on account of the expansion in a paper web, especially in the width direction of the paper web due to water. This concept is effective to a multicolor printing system using many types of paper web.
In newspaper printing works, a part of printing plates should be frequently replaced by a new plate because the newspaper composition depends on distributing area and the information currently reported. Normally used printing systems need to temporarily stop the printing operation to perform this partially replacing work of the printing plate, and after this work to start the printing operation. During this replacing work, the change of the printing speed, i.e., deceleration, stop and acceleration, affects the stretching force applied to the paper web in its longitudinal direction. This will cause register errors in the longitudinal (traveling) direction of the paper web in multicolor printing. Further fine register errors generated during from the plate producing step to the plate setting step are magnified to undesirable register errors which produce many damaged papers.
A conventional B--B type printing apparatus includes divided plate cylinders each of which is provided with a drive unit as shown in FIG. 18. This type cylinder drive unit can not resolve the generation of undesirable idle rotation. FIG. 18 shows a partially sectional plan view of two sets of divided plate cylinders and blanket cylinders. One plate cylinder is divided into an inside plate section PCa (PCa') and an outside plate section PCb (PCb'). The divided cylinder PCa, PCb and a blanket cylinder BC are oppositely arranged between side frames 203 and 204, and they can be moved close to or apart from each other. The external diameter of the blanket cylinders BC, BC' is slightly larger than that of the divided plate cylinders PCa, PCb, PCa', PCb'.
The drive unit shown in FIG. 18 includes a power transmission gear 205 connected to a power unit, a first gear 206 connected to the power transmission gear 205 and fixed to one end of the shaft of the inside plate cylinder PCa, and a second gear 207 connected to the first gear 206 and fixed to one end of the shaft of the blanket cylinder BC. According to this gear engagement, the inside plate cylinder PCa and the blanket cylinder BC are in close with each other and respectively rotated in the counter directions. Since the inside plate cylinder PCa having a smaller diameter functions as a driving roller which drives the blanket cylinder BC having a larger diameter, the driven cylinder BC does not generate the undesirable idle rotation.
The second gear 207 is further engaged with a third gear 208 rotatably mounted on one end of the shaft of the blanket BC'. The third gear 208 is engaged with a fourth gear 209 fixed to one end of the shaft of the inside plate cylinder PCa'. The fourth gear 209 is engaged with a driven gear- 210 fixed to one end of the shaft of the blanket cylinder BC'. According to this gear engagement, the inside plate cylinder PCa' and the blanket cylinder BC' are in close with each other and respectively rotated in the counter directions. Since the inside plate cylinder PCa' having a smaller diameter functions as a driving roller which drives the blanket cylinder BC' having a larger diameter, the driven cylinder BC' does not generate the undesirable idle rotation.
On the other hand, the outside plate cylinders PCb and PCb' are provided with driven gears 212 and 214 through their shafts, respectively. The driven gears 212 and 214 are respectively engaged with gears 211 and 213 fixed to the other end of the shafts of the blanket cylinders BC and BC'. According to this gear engagement, since the outside plate cylinders PCb and PCb' having a smaller diameter function as driven rollers which are driven by the blanket cylinders BC and BC' having a larger diameter, the driven cylinders PCb and PCb' generate the undesirable idle rotation so that double lines and images are printed.